1. Technical Field
This invention relates to pipes. More particularly, it relates to pipes for monitoring groundwater and the like at multiple levels below a single site on the surface of the ground
2. Description of the Prior Art
There are many situations where it is necessary to monitor groundwater in aquifers at multiple levels below the surface. For example, improperly constructed toxic waste storage sites can contaminate groundwater below the site as rain percolating through the earth leaches toxic substances from the dumped materials. Successful confinement of contaminated groundwater requires ongoing monitoring of the quality, quantity and movement of the water. One method of accurately monitoring multiple groundwater levels below a single site on the surface of the ground is to sink separate drill holes to each of the desired levels and install single channel pipes in each hole. Monitoring instruments, such as for sampling ground water, testing permeability, injecting tracers, or measuring water pressure, can then be lowered into the respective pipes for monitoring one of the aquifers as desired. Flow of groundwater up or down the drill holes between aquifers can be prevented by filling all but the deepest portion of each hole with a bentonite or grout sealing compound. A major disadvantage of this multiple hole method is that it requires a great deal of drilling, which is very expensive and time consuming.
A second method for monitoring groundwater at multiple levels below a site involves sinking a single large diameter drill hole to the deepest level to be monitored, and placing multiple single channel pipes of varying lengths into the hole, each pipe terminating at one of the levels to be monitored. The drill hole is backfilled with alternate layers of sand and sealing compound, the sand surrounding the open end of each monitoring pipe where groundwater is to be sampled, and the sealing compound sealing the drill hole between the monitored levels. The disadvantage of this second method is that it requires an expensive large diameter hole, and precise delicate backfilling of the hole to seal the monitored levels from each other without damaging or dislodging the pipes.
The third method for monitoring groundwater at multiple levels a site involves placing a bundle of tubes contained within a pipe casing into a single, smaller diameter drill hole extending to the deepest level of the site to be monitored. Each tube extends to a different depth in the casing, so that water can be drawn from different depths in the drill hole. The interval of drill hole associated with each tube is isolated from above and below by packers that expand so that the annular space between the casing and the wall of the bore hole is sealed over specified intervals. Each of the lengths of tubing within the casing extends continuously from its respective sampling port up to the top of the casing. Thus, each tube must be cut to length during assembly of the device. The casing is divided into sections of manageable length which are coupled together and lowered into the drill hole. As each section of the casing is lowered into the drill hole, the bundle of tubes extending therefrom must be carefully guided through the next section of casing to be placed in the drill hole. Thus, this third method requires exacting, time consuming and correspondingly expensive installation and assembly at the site of the drill hole. Furthermore, the use of separate tubes within the casing requires that each tube be of relatively small diameter, thus limiting the size of monitoring instruments which can be lowered down the tubes.